Recently, two-dimensional materials such as molybdenum disulphide (MoS2) have been demonstrated to realize field effect transistors (FET) with a large current on-off ratio. However, the carrier mobility in backgate MoS2 FET is rather low (typically 0.5–20 cm2/V·s). Here, we report a novel field-effect Schottky barrier transistors (FESBT) based on graphene-MoS2 heterojunction (GMH), where the characteristics of high mobility from graphene and high on-off ratio from MoS2 are properly balanced in the novel transistors. Large modulation on the device current (on/off ratio of 105) is achieved by adjusting the backgate (through 300 nm SiO2) voltage to modulate the graphene-MoS2 Schottky barrier. Moreover, the field effective mobility of the FESBT is up to 58.7 cm2/V·s. Our theoretical analysis shows that if the thickness of oxide is further reduced, a subthreshold swing (SS) of 40 mV/decade can be maintained within three orders of drain current at room temperature. This provides an opportunity to overcome the limitation of 60 mV/decade for conventional CMOS devices. The FESBT implemented with a high on-off ratio, a relatively high mobility and a low subthreshold promises low-voltage and low-power applications for future electronics.

We use density-functional theory and the nonequilibrium Green's function method as well as phonon dispersion calculations to study the thermal conductance of graphene nanoribbons with armchair and zigzag edges, with and without hydrogen passivation. We find that low-frequency phonon bands of the zigzag ribbons are more dispersive than those of the armchair ribbons and that this difference accounts for the anisotropy in the thermal conductance of graphene nanoribbons. Comparing our results with data on large-area graphene, edge effects are shown to contribute to thermal conductance, enhance the anisotropy in thermal conductance of graphene nanoribbons, and increase thermal conductance per unit width. The edges with and without hydrogen passivation modify the atomic structure and ultimately influence the phonon thermal transport differently for the two ribbon types.

No abstract

No abstract

The effects of sulfur passivation on HfO2/GaSb MOS capacitors (MOSCAPs) with neutralized and unneutralized (NH4)2S solutions of varied concentrations were investigated. Treatment with neutralized (NH4)2S aqueous solutions reduced the interface trap density (Dit) by ∼23%, improving the effects of sulfur passivation and producing a smoother interface compared with that obtained by treatment with unneutralized (NH4)2S aqueous solutions. The improved performance of GaSb MOSCAPs is attributed to solution neutralization rather than the change in concentration because the distributions of Dit were similar for samples treated with (NH4)2S solutions of different concentrations.

We perform computer simulations to explore the suprastructures and their formation mechanism in the length-dependent assembly of a stiff polymer chain on the carbon nanotube surface. Three types of local conformations, that is, helical wrapping along the nanotube threadline, nonhelical loop, and straight extension along the nanotube, are identified in the very stiff polymer, depending on its length. It is revealed that the high elastic energy penalty and the large length of a long stiff polymer hinder its conformation transition on the nanotube, which impairs the match between the polymer beads and the structural details of the underlying nanotube surface and thereby weakens the polymer-nanotube interaction. A preferred chain length with an energy minimum is documented for the first time in the self-assemble of a stiff polymer at the nanotube interface. These data significantly advance our understanding of the superstructure formation by self-assembly of various chain-like molecules (e.g., polymer, surfactants, DNA, peptides, etc.) on carbon nanotube.

No abstract

No abstract